The global atmospheric electric circuit, solar activity and climate change

The study of the global atmospheric electric circuit has advanced dramatically in the past 50 years. Large advances have been made in the areas of lightning and thunderstorm research, as related to the global circuit. We now have satellites looking down on the Earth continuously, supplying information on the temporal and spatial variability of lightning and thunderstorms. Thunderstorms are electric current generators, which drive electric currents up through the conducting atmosphere. They maintain the ionosphere at a potential of similar to+ 250 kV With respect to the Earth's surface. The global electric circuit is completed by currents similar to2 pA/m(2) flowing through the fair weather atmosphere, remote from thunderstorms, and by transient currents due to negative cloud-to-ground lightning discharges. The time constant of the circuit, similar to > 2 min, demonstrates that thunderstorms must occur continually to maintain the fair weather electric field. New discoveries have been made in the field of sprites, elves and blue jets, which may have a direct impact on the global circuit. Our knowledge of the global electric circuit modulated by solar effects has improved. Changes to the global circuit are associated with changes of conductivity linked with the time-varying presence of energetic charged particles, and the solar wind may influence the global electric circuit by inferred effects on cloud microphysics, temperature, and dynamics in the troposphere. We now have a better understanding of how the conductivity of the atmosphere is influenced by aerosols, and how this impacts our measurements of the fair-weather global circuit. The global atmospheric electric circuit is also beginning to be recognised by some climate researchers as a useful tool with which to study and monitor the Earth's changing climate. (C) 2000 Elsevier Science Ltd All rights reserved.